1. Field of the Invention
The present invention relates to a long fiber-reinforced polypropylene resin composition and its moldings. Precisely, the invention relates to a long fiber-reinforced polypropylene resin composition and its moldings which have a high rigidity, impact resistance and durability and especially have extremely good repeated impact resistance and creep resistance, and are therefore suitable for various parts including automobile parts and other industrial parts.
2. Description of the Related Art
Long fiber-reinforced polypropylene resin compositions that are generally prepared by impregnating a continuous reinforcing long fiber bundles with a molten polypropylene resin, then pultruding it, and pelletizing it into pellets having a length of from 2 to 50 mm can be formed into good moldings having high mechanical strength and good impact resistance, and they are widely used, for example, for automobile parts and industrial parts. However, when the moldings are loaded with repeated shocks, their repeated impact resistance is unsatisfactory, and, in addition, their creep resistance at high temperatures is also unsatisfactory. At present, therefore, their applications are limited.
In International Patent Laid-Open No. WO/99/11708, proposed are automobile interior parts having improved surface scratch resistance, which are formed by molding a composition that comprises a crystalline propylene-ethylene copolymer composed of homopolymer segments having an isotactic pentad fraction (P) of at least 96% and Mw/Mn (Q) of at most 6 and propylene-ethylene copolymer segments, and contains ethylene-propylene copolymer rubber, talc and long glass fibers. As a result of our investigations, however, we, the present inventors have found that the rigidity, the impact resistance and the durability of the moldings proposed are not as yet satisfactory.
Not known at present, a long fiber-reinforced polypropylene resin composition capable of being formed into good moldings that have a high rigidity, impact resistance and durability and especially have more improved, repeated impact resistance and creep resistance is desired.
The object of the present invention is to provide a long fiber-reinforced polypropylene resin composition and its moldings, which solve all the inconveniences noted above and have a high rigidity, impact resistance and durability, especially having much improved repeated impact resistance and creep resistance, and which are therefore suitable to various parts including, for example, automobile parts and other industrial parts.
We, the present inventors have assiduously studied to solve the problems mentioned above. As a result, we have found that, when a modified propylene homopolymer or a modified propylene-ethylene copolymer which is prepared by modifying a specific propylene homopolymer or a specific crystalline propylene-ethylene copolymer with an unsaturated carboxylic acid or its anhydride, or a mixture which comprises the modified propylene homopolymer or the modified propylene-ethylene copolymer and the non-modified, specific propylene homopolymer or specific crystalline propylene-ethylene copolymer is used as a matrix polymer, and when a specific amount of the matrix polymer is mixed with a specific amount of glass fibers having a specific length, then the resulting, long fiber-reinforced polypropylene resin composition is extremely useful for solving the above-mentioned problems. On the basis of this finding, we have completed the present invention.
The present invention reside in following items:
(1) A long fiber-reinforced polypropylene resin composition, which comprises from 35 to 75% by weight of a matrix polymer and contains from 25 to 65% by weight of long glass fibers having a length of from 2 to 50 mm, and in which the matrix polymer is a modified propylene homopolymer or a modified propylene-ethylene copolymer prepared by modifying a propylene homopolymer having an isotactic pentad fraction (P) of at least 96% and Mw/Mn (Q) of at most 6, or a crystalline propylene-ethylene copolymer composed of homopolymer segments having an isotactic pentad fraction (P) of at least 96% and Mw/Mn (Q) of at most 6 and propylene-ethylene copolymer segments, with an unsaturated carboxylic acid or its anhydride, or a mixture of the modified propylene homopolymer or propylene-ethylene copolymer and the non-modified propylene homopolymer or crystalline propylene-ethylene copolymer, and has a melt flow rate (230xc2x0 C., 21.18 N) of at least 50 g/10 min.
(2) The long fiber-reinforced polypropylene resin composition of above 1, wherein the crystalline propylene-ethylene copolymer is composed of homopolymer segments having an isotactic pentad fraction (P) of at least 96%, Mw/Mn (Q) of at most 6 and a hexane extraction of at most 0.8% by weight, and propylene-ethylene copolymer segments, and the modified propylene-ethylene copolymer is prepared by modifying the crystalline propylene-ethylene copolymer with an unsaturated carboxylic acid or its anhydride.
(3) A long fiber-reinforced polypropylene resin blend composition produced by blending the long fiber-reinforced polypropylene resin composition of any one of above 1 or 2, with a propylene homopolymer and/or a propylene-based block copolymer.
(4) Moldings of the long fiber-reinforced polypropylene resin composition of any one of above 1 or 2, or moldings of the long fiber-reinforced polypropylene resin blend composition of above 3.
From the viewpoint of improved rigidity, impact resistance and durability of the moldings of the resin composition of the invention, the starting polymer that gives the modified propylene homopolymer to be in the resin composition is a propylene homopolymer having an isotactic pentad fraction(P) of at least 96% and a ratio(Q) of weight-average molecular weight Mw/number-average molecular weight Mn of at most 6; and the starting polymer that gives the modified propylene-ethylene copolymer to be therein is a crystalline propylene-ethylene copolymer composed of homopolymer segments having an isotactic pentad fraction (P) of at least 96% and a ratio (Q) of weight-average molecular weight Mw/number-average molecular weight Mn of at most 6, and propylene-ethylene copolymer segments, preferably a crystalline propylene-ethylene copolymer composed of homopolymer segments having an isotactic pentad fraction (P) of at least 96%, a ratio(Q) of weight-average molecular weight Mw/number-average molecular weight Mn of at most 6 and a hexane extraction of at most 0.8% by weight, and propylene-ethylene copolymer segments.
The isotactic pentad fraction(P) referred to herein indicates the isotactic fraction of pentad units in the molecular chain of the polymer, and this can be measured through 13C-NMR, for example, according to Macromolecules 8, 687 (1975). The weight-average molecular weight Mw and the number-average molecular weight Mn of the polymer can be measured through gel permeation chromatography (GPC).
For the matrix polymer to be in the resin composition of the invention, usable is any of the above-mentioned propylene homopolymer and crystalline propylene-ethylene copolymer composed of homopolymer segments and propylene-ethylene copolymer segments (these are hereinafter referred to as propylene (co) polymers). From the viewpoint of the rigidity, the impact resistance and the durability of the moldings of the resin composition, however, preferred is the latter copolymer. More preferred is a crystalline propylene-ethylene copolymer composed of homopolymer segments having an isotactic pentad fraction (P) of at least 96%, Mw/Mn (Q) of at most 6 and a hexane extraction of at most 0.8% by weight, and propylene-ethylene copolymer segments.
Producing the propylene (co) polymers is not specifically defined, for which is employable any known method. One example of producing them comprises homopolymerizing propylene or polymerizing propylene followed by copolymerizing propylene with ethylene, in the presence of a high-stereospecificity catalyst such as that disclosed in Japanese Patent Laid-Open No. 269124/1996, concretely comprising a solid catalyst component that contains at least magnesium, titanium and halogen atoms and a polycarboxylate, along with an organoaluminum compound such as triethylaluminium, and an electron donor compound such as t-butyltriethoxysilane. In order to control the hexane extraction to fall within the range as above, slurry polymerization or copolymerization is preferred.
For producing the modified propylene homopolymer and the modified propylene-ethylene copolymer for use in the invention (these are hereinafter referred to as modified propylene (co)polymers), for example, employable is a method of melt-kneading 100 parts by weight of the starting polymer along with from 0.1 to 5 parts by weight of an unsaturated carboxylic acid or its anhydride and from 0.01 to 0.5 parts by weight of an organic peroxide.
Apart from this, also employable is a method of melt-kneading 100 parts by weight of the starting polymer along with from 1 to 10 parts by weight of a commercially-available modified propylene polymer that contains from 1 to 10% by weight of an unsaturated carboxylic acid or its anhydride introduced thereinto, and from 0.01 to 0.5 parts by weight of an organic peroxide; or a method of melt-kneading 100 parts by weight of a molten mixture that comprises 100 parts by weight of the starting polymer and from 0.01 to 0.5 parts by weight of an organic peroxide, along with from 1 to 10 parts by weight of a commercially-available modified propylene polymer that contains from 1 to 10% by weight of an unsaturated carboxylic acid or its anhydride introduced thereinto.
From the viewpoint of improved rigidity, impact resistance and durability of the moldings of the resin composition of the invention, the melt flow rate (230xc2x0 C., 21.18 N; hereinafter referred to as MFR) of the modified propylene (co)polymers is preferably at least 50 g/10 min.
The unsaturated carboxylic acid and its anhydride include, for example, acrylic acid, methacrylic acid, maleic acid, nadic acid, fumaric acid, itaconic acid, maleic anhydride, nadic anhydride, and itaconic anhydride. From the viewpoint of easy reinforcement of the modified (co)polymer with glass fibers, preferred is maleic anhydride.
The modified propylene (co)polymers may be produced prior to the process of producing the long fiber-reinforced polypropylene resin composition (A) that is described in detail hereinunder, or may be produced in the process of melt-kneading the matrix polymer to give the long fiber-reinforced polypropylene resin composition (A).
The matrix polymer to give the long fiber-reinforced polypropylene resin composition (A) of the invention may be the modified propylene (co)polymer alone, or may be a mixture of the modified propylene (co)polymer and the non-modified, starting propylene (co)polymer. From the viewpoint of improved rigidity, impact resistance and durability of the moldings of the resin composition, it is desirable that the matrix polymer comprises, as the essential ingredient (in an amount of more than 50% by weight), the modified propylene (co)polymer, but more preferably, all the matrix polymer is the modified propylene (co)polymer alone. For examples of the non-modified propylene (co)polymer that may be in the matrix polymer, referred to are those mentioned hereinabove for the starting polymers to give the modified propylene (co) copolymers. In case where the matrix polymer is a mixture of the modified propylene (co)polymer and the non-modified propylene (co)polymer, it is desirable that the MFR of the mixture is at least 50 g/10 min.
The starting material for the long glass fibers having a length of from 2 to 50 xcexcm to constitute the long fiber-reinforced polypropylene resin composition of the invention may be long glass fiber bundles, which are, for example, commercially-available glass rovings. In general, their mean fiber diameter falls between 4 and 30 xcexcm; the number of filaments constituting one fiber bundle falls between 400 and 10,000; and the the tex yarn number count of one fiber bundle falls between 300 and 20,000 g/km. Preferably for use herein, the mean fiber diameter of the fiber bundles falls between 9 and 23 xcexcm, and the number of filaments constituting one fiber bundle falls between 1,000 and 6,000. For enhancing their reinforcing ability, the fiber bundles are preferably treated with silane coupling agent on their surface. Thus processed, the fiber bundles enjoy good interlayer adhesion to resin.
For producing the long fiber-reinforced polypropylene resin composition, employable is any known method of melt pultrusion. Generally employed is a method in which a molten resin of the matrix polymer is fed from an extruder where it is prepared, into an impregnation die equipped at the top of the extruder, while long glass fiber bundles are passed through the die to thereby impregnate the fiber bundles with the molten resin, and the thus-impregnated fiber bundles are drawn out through a nozzle, and then pelletized into pellets having a length of from 2 to 50 mm. As so mentioned hereinabove, also employable is a method in which the propylene (co)polymer is dry-blended with an unsaturated carboxylic acid or its anhydride, and an organic peroxide, and the resulting blend is put into the hopper of the extruder. In this, the propylene (co)polymer is applied to long glass fiber bundles while it is modified.
For impregnating glass fiber bundles with the matrix polymer, any known method is employable so far as it ensures good resin impregnation. For example, employable is any of a method of letting glass fiber bundles on the surface a resin spreader while in contact with it under tension to thereby impregnating them with a molten resin (Japanese Patent Publication No. 37694/1988); or a method of letting glass fiber bundles through a pair of opening pins equipped in an impregnation die while not in contact with the pins to thereby impregnate them with a molten resin (International Patent Laid-Open No. WO97/19805) Of the two, preferred for the invention is the latter method as the fiber bundles impregnated therein are fluffed little while they are taken up at high speed.
The glass fiber content of the long fiber-reinforced polypropylene resin composition falls between 25 and 65% by weight, preferably between 35 and 55% by weight of the composition, from the viewpoint of improved rigidity, impact resistance and durability of the moldings of the composition. The long fiber-reinforced polypropylene resin composition may be directly molded as it is, but may be molded after diluted with any other propylene homopolymer and/or propylene-based block copolymer (B) not containing long glass fibers. For the propylene-based block copolymer that serves as the diluent (B), usable is a crystalline propylene-based block copolymer having a propylene content of at least 70% by weight and copolymerized with an xcex1-olefin except propylene, for example, with ethylene, 1-butene, 1-pentene or the like. From the viewpoint of improved rigidity, impact resistance and durability of the moldings of the resin composition, preferred for the diluent is such a crystalline propylene-based block copolymer of which the homopolymer segments have an isotactic pentad fraction(P) of at least 96% and Mw/Mn (Q) of at most 6. The diluent (co)polymer may be in any form of pellets, granules, flakes and powders, and its morphology is not specifically defined. For it, however, preferred are pellets.
The long fiber-reinforced polypropylene resin composition may be dry-blended with the diluent (B). For making the reinforcing fibers keep their length in the blend composition and for further enhancing the stiffness, the impact resistance and the durability of the moldings of the composition, it is rather preferable that the composition is, after prepared by dry-blending the components, directly fed into a molding machine such as an injection-molding machine, not being let into an extruder. The blend ratio of the diluent (B) is determined, depending on the glass fiber content of the long fiber-reinforced polypropylene resin composition and on the glass fiber content of the final moldings of the composition, and may fall between 20 and 85% by weight from the viewpoint of improved rigidity, impact resistance and durability of the moldings. Apart from the diluent (B), any other additive of antioxidant, light stabilizer, UV absorbent and antistatic agent may be added to the resin composition, if desired.
For forming the long fiber-reinforced polypropylene resin composition or the blend composition into moldings, employable with no limitation is any known molding method of, for example, injection molding, extrusion molding, blow molding, compression molding or injection compression molding. For it, however, preferred is injection molding, compression molding or injection compression molding. The resulting moldings have many applications in various fields, and are especially favorable for automobile parts and other industrial parts.